Copolymers of methacrolein



United States Patent 2,996,481 I g COPOLYMERS 0F METHA'GRQL-EIN RobertLee Eifert and Barnard Mitchel Marks; Wilmington, Del., assignors to E.I. du Pont de Nemours and Company, Wilmington, DeL, a corporation ofDelaware 1 No Drawing. Filed Jan. 24, 1958, Ser. No. 710,850 r 9(Slaims. ($1. 260-67) :lfh present invention relates to novel polymericproducts and more particularly to novel copolymers of meth- It is anobject of the present inyention to prepare high I molecular weight,soluble copolymers of methacrolein. cohtaining a high percentage ofmethacrolein. It is another object of the present invention to preparemolecular Weight copolymers of niethaerole-inand ethyleuicallyunsaturated monomers, said copolymers havtag a substantially linearmolecular configuration and beifigsoluble inorganic solvents.

It a further object of the present invention to pre= gate high molecularweight eopolymers of methaerolein ethylenically unsaturated monomers,said gcopoly having improved melt flow proper-ties. Other ob eeps villbecome apparent hereinafter. V

In accordance v'vitli the present invention it has been uncovered thatniethacrolein can be copolymerizetl with a comonoiner of the classconsisting of compounds haviiig vinylic unsaturation and compoundshaving o ealkendioic unsaturation to give rise to tough, linear,copolymers of high molecular weight containing a larger percentage ofmethacrolein, which are soluble in organic solvents and haveappreciablemelt flow at temperatures above the softening point of thepolymer. Examples of these comonomers are esters and nitriles ofacrylic, methaerylie, fuinaric and maleic acid; etc; ,The comonomer ispreferably employed in quantities of l to 25 percent by Weight of thetotal monomer concentration;

More specifically, nov'el copolymers of the present in vention includethose in which the comonomer may he one or more of the esters of acrylicand methacrylic acid such as the methyl, ethyl, ethoxyethyl, propyl,butyl,

hexyl, benzyl, octyl, isooctyl, d'o'decyl ester, and esters of fumaricand maleic acid such as the dimethyl, diethyl, methylethyl, dipropyl,propylmethyl, propylethyl ester as vyell as the nitriles of these acids.Preferred esters are those which have from 1 to 5 carbon atoms in theester oup- The methacrolein copolymers of the present invention arecharacterized by high molecular weights, ranging from inherentviscosities of 03 to 3 as measured in 0.5% concentrations at 35 6.; inpyridine, by softening points in therange of 190 to 240 (2.; bysolubility in organic solvents such as dimethyl formamide and pyridine;and by improved melt flow at temperatures above the softening point ascompared to the homopolymer of methacrolein. It was surprisingly foundthat small quantities of the acrylic comonomer caused a significantincrease in the melt flow of the polymer and thus greatly increased theease of fabrication of methacrolein polymers without significantlyafiectiug the mechanical properties of the i6 ymer. 'Ihe polymers of thepresent invention con tain from 1 to 25% of the acrylic comonomer.Although it is possible to prepare cop'oly'mers with a centration ofcomonomer, the physicalproperti'es of e copolymers do not show thecombination of high rig y and toughness as do the copo1ymers,,containing front to 25% of the acrylic comonomer. Furthermore the ftention of properties with increasing temperature g'r aflyreduced as thecommenter concentration is significantly increased beyond 25%. v A

The methacrolein copolymers of the present invention are prepared bycopolymerization of amiXture of the monomers in anaqueous medium inwhich the monomers are soluble but in Which the polymer is not solubleand from yvhich the polymer precipitates out to forma dis persion. Theformation ofa polymer solution or the formation of a coagulated polymermass must be avoided to prevent the formation of a crossqinlced polymerwhich is insoluble and intractible and thus not suited for fabricationinto useful articles and shapes. The formation of the cross-linkedintractible polymer is believed to result from the further reaction ofpendent aloe groups in the polymer chains; such reaction can readilyoccur yvhere the polymer re niains in solution. By poly merizing themonomer to finely divided polymer particles; the cross-linking reactionis believed to be reduced to a riiinimum and the polymerization resultsin the formation of substantially linear polymers. formation ofsubstantially linearpolymers is achieved by employing} polymeriiati ofiinediuifi in Which the monomer i oltlblo and in vv'hich the polymer isinsoluble and carry out the polymerization under conditions favoring thef tion of dispersed polymer. The catalyst employed to initiate theaddition copolymerization of methacrolein is a free radical catalystsoluble iii the polymerization medium. Although a large variety of freeradical catalysts may be employed, such as peroxides for example; it isgenerally preferred toemploy redox catalysts, since these catalysts aresoluble in aqueous media, and are furthermore less dependent ontemperature withrespe'ct to the rate of free radical formation. Redoxcatalysts which are suitable for the polymerization may be formed bythereaction ofsoluble multivalent metal salts in their higher valencestates or by the reaction of any other soluble oiridizing agents suchasinorganic peroxides, examples of which are hydrogen peroxide andpotassium persulfate; with the alkali metal orammonium salt of; reducinginorganic anions such as thefhypophosphite, thiosulfate; sulfit,bisulfite or hyposulfite ions, It was further found; that in thepolymerization of methacrolein the oxidizing agent could be omitted andthat the copolymerization of methacr'ole in comonomers of the presentinvention could be initiated by simply adding the reducing agent to thefeactionjne'diurn. A particularly preferred caba lyst being alkali metalor ammonium bisulfite. The Quantity of the catalyst employed, calculatedon thebasis of the reducing agent, is critical and should not exceed9.005 mol percent of the total monomer concentration. Higherconcentrations lead to the formation of lower molecular Weight polymers.A suitable catalyst canteen. tiat'ion range is from 0.001 to 0.005 molpercent.

The polymerization ispreferabIy cameras i presence of a finely dividedsolid such, as silica, t iirconia, alumina, ands'irnilar materials. Thead of such compounds as silica aids in the formation of h copolymers forreasons presently not clearly understood, but passing the presence ofthe solid aids the rat; inane-n of stable polymer dispersions. The solidhecti only be employed in minute quantities such as 0.005% by weight ofthe polymerization medium. 7

Since the solubility of rilethacrolein and the acrylic co? monomers inwater is limited and more concentrated so: lutions of methacrolein andacrylic :rnou are do si-rable in order to prepare metha'crbleifi eon/menhaii at eflicient polymerization 1 to 5 carbon atoms such as methanol,ethanol, butanols, isopropanol, etc. The quantity of the alcoholemployed twill depend on the, amount of the monomers that is required tobe in solution. The monomer concentration in the reaction medium ismaintained in a range of 7 to 210% and preferably f'rom20 to 40% byweight 'of'the medium. Higher concentrations cause coagulation of'the'dispersed'polymer. If desirable, the concentration may the slightlyincreased by the addition of dispersing agents which inhibit thecoagulation of the polymer formed.

The polymerization'is preferably carried out'at temj'pe'ratures below 50C. and preferably at temperatures of j to 35 C. in the substantialabsence of oxygen. The monomers employed should be free from impurities.It is therefore highly desirable to purify commercially availablemethacrolein by distillation or treatment with ab- :sorbents whichwillremove the impurities prior to. use. in

the polymerization. The polymerization is furthermore preferably carriedout in a slightly acidic medium. The copolymers of the present inventionare characater- Lized and evaluated in the examples below by their in-Ehe'i'ent viscosity, flow numbers and softening points. As

stated hereinabove, thejyiscosity of the copolymeris tie-- termined from0.5% concentrations of the" copolymer in pyridine at 35 C. The inherentviscosity of "themethacrolein 'copolymers is' calculated from thefollowing equation where t is the viscosity of the solvent, and t theviscosity 4 points given for the copolymers of the present inventionwere obtained by recording the temperature at which the polymer leaves amolten trail when moved across the surface of a heated block underslight positive pressure. The temperature of the blockis increased atthe rate of 1 C. per-minute.

The invention is'further illustrated by the following examples:

Example 1 Into a glass stoppered Erlenmeyer flask was charged undernitrogen with mild agitation 96 ml. of deoxygenated, distilled-water,0.4 ml. of;Ludox,' a commercially available aqueous dispersion ofcolloidal silica containing approximately 30% of silicon dioxide, 100ml. of

methanol, 97 ml. ofm'ethacrolein, 3 of ethyl acrylate, 3.6 ml. of a 1%aqueous solution of sodium bisulfite as the catalyst, corresponding to acatalyst concentration of 1.15 x 10's? moles per liter of reactionmedium,

and fourdrops of acetic acid to bring the pH of the reaction mixture to4.4. On'addition of the ingredients, the reaction mixture was allowed tostand for a period of 20 To the resulting polymer dispersion was addedml. of a 2% solution of- 2,6-di-tert.butyl-4-methyl-phenol to stabilizethe polymer. The dispersion was then coagulated by the addition ofsodium sulfate. The polymer was collected by filtration,- washed withwater and methanol, treated again with the same quantity of antioxidantand dried in a vacuum oven; A white solid polymer com"- prising 62.7% ofthe starting material, having'aninherent viscosity of 1.11 and asoftening point of approximate- 'l-y- 205 C. was obtained. The flownumbers of thepolysuitable for plastic applications since such polymersare diificult tofabricate by melt extrusion or injection molding. Thecopolymers of the present invention arethose which have inherentviscosities in the range of 0.3 to 3.0 and preferably have inherentviscosities in the range of 0.5 to 1.5. A further measure of thesuitability of'a polymer for fabrication by melt extrusion or injectionmolding is a. measure of the melt flow of the polymer. The melt flow ofthe methacrolein copolymers of the present invention is measured by flownumbers, which are a measure of the quantity of molten polymer in gramswhich will flow through an orifice 0.0823" in diameter over a period of10 minutes at a temperature of 275 .C. when subjected to a pressureexerted by a 3800 g. weight on a piston 95 in diameter. The melt flowequipment employed in the present invention is similar to the equipmentemployed in the determination of melt index, which is described indetailin ASTM-D-1238-52T, except for thedifferences in temperature andweight stated above. additional characterization of the polymer is itsmelt ing point. However, since the methacrolein copolymers of thepresent invention are amorphous, they do not have the sharp meltingpoint that can be observed with crysta1 line polymers but show a gradualchange from the solid to the liquid stage with increasing temperature.The term softening point is therefore more appropriate for thecopolymers of the present invention. The softening mer after7, 10, 15and ZO-minutes were measured to be 0.35, 0.63, 1.1 and A homopolymer ofmethacrolein prepared with the identical polymerizationrecipe was foundto have a softening point at 213 C. and flow numbers after 7, 10,15 and20 minutes of 0.2, 0.27, 0.49 and 0.78. The polymer could be molded intostilf, transparent films by heating the polymer to a temperature, of 250to 275 C.

Example II Employing the procedure of Example I, 5% of ethyl acrylate,basedon the total monomer concentration, was copolymerized withmethacrolein. The weight of the resulting polymer was 26.4 g.corresponding to a 62.2% conversion. The copolymer was found to have aninher ent viscosity of 1.09, a softening point at approximately 205 C.,and had flow numbers of 0.5, 0.9, 1.4 and 2.0

s after 7, '10, 15 and 20 minutes exposure at 275 C.

respectively.

Example 111 Employing the procedure of Example I, 12% of ethyl acrylatewas copolymerized with methacrolein employ- Example I V Employing theprocedure of Example I, 10% of ethyl acrylate, based on the totalmonomer concentration, was copolymerized with methacrolein. The weightof the washed and dried copolymer was 23 g. correspond-1 ing to a 54.4%conversion. The polymer was found to: have an inherent viscosity of 1.06and W numbers of 5 1.1, 1.4, 2.0 and 3.0 after 7-, 10, 15 and 20 minutesexposure at 275 C. respectively.

Example V Employing the procedure of Example I, 25% of ethyl aetylatebased on the total monomer concentration was copolymerized withmethacrolein employing a catalyst concentration of 0.8 10- moles perliter. The weight of the washed and dried product was 15 g.corresponding to a 35% conversion. The inherent viscosity of thecopolymer was measured to be 1.4 and the softening point was found to be190 C. The melt flow of the copolymer, as measured in flow numbers at275 C., was found to be 0.8, 2.0, 2.9 and 5.3 after 7, 10, 15 and 20minutes exposure respectively.

Example VI Employing the procedure of Example I, 88 m1. of methacroleinwas copolymerized with 12 ml. of butyl acrylate employing a catalystconcentration of 2.3x 10- moles per liter. The weight of the washed anddried product was 53.8 g. corresponding to a conversion of 63.5%. Thecopolymer was found to have an inherent viscosity of 1.05. The melt flowof the polymer as measured in how numbers at 275 C. was found to be 8.1,9.2, 11.4 and 15.6 after 7, 10, 15 and 20 minutes exposure respectively.

Example VII Into a glass stoppered Erlenmeyer flask was charged undernitrogen 60 ml. of deoxygenated, distilled water, 0.1 ml. of Ludox, 100ml. of isopropanol, 45 ml. of methacrolein, 5 ml. of dimethyl-maleate, 5mg. of a 75:25 mixture cobalt oxide and cupric oxide, 2.4 ml. of a 1%solution of sodium bisulfite, 10 mg. of potassium persulfate, and twodrops of acetic acid to make the reaction medium acidic. On standing for20 hours, 35 m1. of a 2% aqueous solution of2,6-di-tert.butyl-4methylphenol was added and the reaction mixture wascoagulated with 'Na SO the polymer collected by filtration, washed,treated with a similar portion of antioxidant and dried. The resultingpolymer weighed 14.3 g. corresponding to a conversion of 34%. Thepolymer was found to have an inherent viscosity of 0.83 and a melt flowas measured by flow numbers at 275 C. of 2, 3, 4.5 and 6.3 at 7, 10, 15and 20 minutes exposure respectively.

Example VIII Into a glass stoppered Erlenmeyer flask was charged 30 ml.of deoxygenated distilled water, 0.1 ml. of Ludoxf 50 ml. ofisopropanol, 45 ml. of methacrolein, 5 ml. of diethyl fumarate, 3 mg. ofa 75:25 mixture of C 0 and CuO, 1.8 ml. of a 1% aqueous solution ofsodium bisulfite, 10 mg. of potassium persulfate and 3 drops of aceticacid to make the reaction medium acidic. On standing for 20 hours, 35cc. of a 2% aqueous solu tion of 2,6-di-tert.butyl-4-methylphenol wasadded and the reaction mixture was agitated to cause coagulation of thecopolymer dispersion. The coagulated polymer was filtered, washed anddried and weighed 11.8 g. corresponding to a 28% conversion. The polymerwas found to have an inherent viscosity of 0.71 and a melt flow asmeasured by flow numbers at 275 C. of 1.3, 1.6, 2.3 and 3.1 at 7, 10, 15and 20 minutes exposure respecn'vely.

Example IX Employing the procedure shown in Example VIII, 45 ml. ofmethacrolein was copolymerized with ml. of acrylonitrile. A copolymerweighing 5.9 g. corresponding to a 14% conversion having an inherentviscosity of 0.81 was obtained.

The methacrolein copolymers of the present invention are high molecularweight resins which on molding, extrusion or casting from solution formrigid, tough, highly transparent shapes suitable for a large variety ofplastic applications. In contrast to the prior art a ena-tantraeopolymergtliey differ in chemical composition aim/er Structure. Thecopolymers of the pre ent inviltibfl nave substantially the mechanicalproperties of linear pe vineth'acroleins and differ from prior linearcopfilymers of methacrolein in'thei'f high inetliacfol'eiii "coarser,which gives rise to the highly useful properties of rigidity andtransparency. They differ from the prior art methacrolein copolymershaving high concentration of methacrolein in their physical structure inthat they are substantially linear polymers as contrasted to thecross-linked structure of prior art polymers, in that they are solublein organic solvents and in that they can be fabricated by melt extrusionand molding techniques. The copolymers of the present invention althoughemploying only small quantities of comonomer are highly improved in meltflow over substantially linear polymethacrolein. This improved melt flowof the methacrolein copolymers with the acrylic monomers is obtainedwithout a significant loss of the solid state mechanical properties ascompared to the homopolymers of methacrolein.

The methacrolein copolymers of the present invention are suitablyemployed in lighting fixtures, ornamental designs, outdoor signs,packaging films and in coating applications. Fibers may be prepared fromthe copolymers of the present invention using melt or solution spinningtechniques.

We claim:

1. A copolymer of monomers consisting essentially of methacrolein and acomonomer of the class consisting of alkyl esters of acrylic acid,fumaric acid and maleic acid, wherein the ester radical contains from 1to 5 carbon atoms, said copolymer containing from 1 to 25 weight percentof said comonomer and having an inherent viscosity, as determined on a0.5 percent solution in pyridine at 35 C., of 0.3 to 3.0.

2. A copolymer of monomers consisting essentially of methacrolein and analkyl acrylate, wherein the alkyl radical contains from 1 to 5 carbonatoms, said copoly mer containing from 1 to 25 weight percent of saidalkyl acrylate and having an inherent viscosity, as determined on a 0.5percent solution in pyridine at 35 C., of 0.3 to 3.0.

3. A copolymer of monomers consisting essentially of methacrolein andethyl-acrylate, said copolymer containing from 1 to 25 weight percent ofsaid ethyl acrylate and having an inherent viscosity, as determined on a0.5 per cent solution in pyridine at 35 C., of 0.3 to 3.0.

4. A copolymer of monomers consisting essentially of methacrolein and adialkyl fumarate, wherein the alkyl radical contains from 1 to 5 carbonatoms, said copolymer containing from 1 to 25 weight percent of saiddialkyl fumarate and having an inherent viscosity, as determined on a0.5 percent solution in pyridine at 35 C., of 0.3 to 3.0.

5. A copolymer of monomers consisting essentially of methacrolein and adialkyl maleate, wherein the alkyl radical contains from 1 to 5 carbonatoms, said copolymer containing from 1 to 25 weight percent of saiddialkyl maleate and having an inherent viscosity, as determined on a 0.5percent solution in pyridine at 35 C., of 0.3 to 3.0.

6. The copolymer of claim 1 in film form.

7. The copolymer of claim 1 in fiber form.

8. The process of copolymerizing methacrolein and a comonomer of theclass consisting of the nitriles and alkyl esters of acrylic acid,methacrylic acid, fumanic acid and maleic acid, wherein the esterradical contains from 1 to 5 carbon atoms, which comprises polymerizinga mixture of methacrolein and said comonomer with an aqueous mediumcontaining sufiicient of an aliphatic water-miscible alcohol of 1 to 5carbon atoms to maintain said monomers in solution, said methacroleinand monomer being employed in a ratio of 99:1 to 75:25 in aconcentration of 7 to 40% by weight of the medium, said aqueous mediumfurther containing from 0.001 to 0.005

2;996;4 8 1 s 111191 pengent, bssadon the monomers of bisulfite ion, and--Referenes'Cited"in the/ file of this patent, ,3? up to 01105 weightpercent, based on the aqueous medium .gf finely divided silica, at atemperature of 20 t0'35 C:, UNITED- STA B TENTS .in'hhe substantialabsence of oxygen. 2,416,536 Neher et a1. Feb. 25, 1947 @9. The processas set forth in claim 8 wherein the 5 155L622." sw t';' S pt-3,1953.qomonomer is an alkyl acrylate. 2; 657,'1 92' "Miller et a1 Oct;27,1195? I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIUN PatentNo. 2,996,481 August 15, 1961 7 Robert Lee Eifert et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line l4, for "and certain ethylenically unsaturated monomers"read could be copolymerized with acrylic monomers column 3, lines 35 and36, the formula should appear as shown below instead of as in thepatent! column 3, line 42, for "in only" read is only column 6, line 73,after "75:25" insert and Signed and sealed this 9th day of January 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVIDL. LADD Attesting Officer Commissioner of Patents

1. A COPOLYMER OF MONOMERS CONSISTING ESSENTIALLY OF METHACROLEIN AND ACOMONOMER OF THE CLASS CONSISTING OF ALKYL ESTERS OF ACRYLIC ACID,FUMARIC ACID AND MALEIC ACID, WHEREIN THE ESTER RADICAL CONTAINS FROM 1TO 5 CARBON ATOMS, SAID COPOLYMER CONTAINING FROM 1 TO 25 WEIGHT PERCENTOF SAID COMONOMER AND HAVING AN INHERENT VISCOSITY, AS DETERMINED ON A0.5 PERCENT SOLUTION IN PYRIDINE AT 35*C., OF 0.3 TO 3.0.